It seems a number of people have either
1. had problems with past rules interpretations of firearms (eg: balance, workability etc), or
2. feel that the flavour of DnD is incompatible with fireamrs, or
3. Don't see that firearms would have developed in the first place (competing with magic).
A 1. In the excellent Savage Tide AP, I pleaded with my DM to allow "Malachi the Mad", a Swashbuckling Rogue and Captain of the the now beached Sea Wyvern, to use a pistol using the Privateer Press OGL firearms rules <http://www.privateerpress.com/docs/privateer_firearms.pdf>.
He was reluctantly persuaded. Since that time (with at least three fumbles, which fortunately did not end up with Malachi's arm being blow off), and many more holes in the ceiling than dead-eye shots, but 2 or 3 massive criticial sneak attacks, they are consisered a great game success, both in flavour, and balance, by the DM and all the players. On balance, I would have to say that I would be doing more damage had I put the same number of feats into a longbow, but the boomstick is way more fun.
A 2. That really depends on the setting. Even for me, "fireamrs everywhere" is not to my liking. I can't see elves or rural halflings having much to do with them. I can see races that culturally have little to do with arcane magic, but everything to do with metallurgy "giving it a shot" (such as Dwarves, and possibly although unreliably Gnomes).
A 3. See A 2, also consider the "training time" for a non-adventuring mage. One person can make alchemical powder for hundreds of poorly trained militia. The results may normally be on par with the ancient crossbow, but may chance to do more damage on a critical.